The invention relates to a stiffness adjustment mechanism for a seat back or seat base such as used in an automobile.
Automobile seat back or seat base of the type described in German patent DE 297 23 586 U1, utilizes shaped wire springs which extend parallel to the direction of vehicle travel with one end permanently attached to a cross brace of a frame part while the other end is attached to an adjustment member by means of which the separation between the anchoring points may be altered. The known solution allows alteration of seat stiffness by increasing or decreasing the tension. When the tension is changed, there is practically no alteration to the upper surface shape of the seat base or of the seat back. The position or shape of the side bolsters or supports, in particular, does not change.
In another system, it was also suggested that a seat base be provided with alterable side bolsters as well as with a central spring system whose tension may be altered. Thus, the position of the side bolsters or of their upper edge areas can be dislocated or adjusted depending on the hardness of the seat springs so that a higher degree of seat stiffness is related to a higher position of the edge area. Such a solution is useful because a sporty driver who prefers a firm and hard seat also requires good lateral support provided by shaped side bolsters. A comfort-oriented driver, on the other hand, prefers a soft, comfortable seat with less-pronounced side bolsters. With this system, however, two adjustment mechanisms were provided.
The present invention features a tension mechanism for a seat having a frame with a plurality of springs having an undulating shape defining tension belt receiving areas and having a support side. The plurality of springs are attached between two opposing braces in the seat frame.
The tension mechanism includes a plurality of tension belts having first and second ends and disposed in the tension belt receiving areas of the springs and adapted for adjusting a vertical displacement of the support side of each of the plurality of springs. Each of the plurality of tension belts are coupled proximate at least the first end to a tension belt tensioning device adapted to produce more or less tension in the tension belts, wherein the vertical displacement of the support side of each of said plurality of springs is less when the plurality of tension belts are under low tension than when they are under higher tension.
The present invention also provides a seat back or seat base wherein adjustment of the upholstery stiffness in the central area of the seat back or seat base effects a shape change of the central area of the seat shape or back shape and not the side regions of the seat, and wherein the difference between the central seating surface height and the side bolster height is greater for increased seat stiffness than for low seat stiffness, whereby the position of the side bolster itself remains unchanged and need not be adjusted.
The invention creates a side bolster height corresponding to the current seat stiffness without providing an adjustment mechanism for the side bolster. The solution proposed by the invention thus allows simple adaptation of the seat shape to various user wishes without involving great expense or complex mechanisms.